Reptiles of North Carolina
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NC Records

Thamnophis sirtalis - Common Gartersnake


Photo: Steve Hall
Photo: J. Mickey
Photo: K. Bischof
Taxonomy
Class: Reptilia Order: Serpentes Family: Colubridae Subfamily: Natricinae Other Common Name(s): Eastern Garter Snake
Taxonomic Comments: Thamnophis currently consists of 37 species of slender to moderately-sized natricid snakes, ranging widely across most of North America, from Canada through the majority of the United States and Mexico, south to Costa Rica.
Species Comments: Thamnophis sirtalis, the Common Gartersnake, is one of two Thamnophis in North Carolina. This species is one of the most wide-ranging in North America, with populations as far north as the southern end of the Northwest Territories in Canada, extending down both coasts to southern California and southern Florida. They are most common along the Atlantic Coast, Midwest, and West Coast, and rarer in the American Southwest. In North Carolina they are common state-wide, with the exception of the Outer Banks.

Some authors recognize as many as 12 subspecies, with T. s. sirtalis (Eastern Gartersnake) the most widely distributed (and the only one found in North Carolina). However, recent molecular work (Jones et al. 2023, among others) has shown that phenotypic differences between subspecies do not reflect shared evolutionary history. Instead, four evolutionary lineages are found across the species's range.

The generic epithet Thamnophis is derived from the Greek thamnos ("bush") and ophio ("snake"). The specific epithet sirtalis is new Latin, meaning "like a garter".

Taxonomic References: Fitch (1980).
Identification
Description: Common Gartersnakes are medium-to-moderately-sized snakes with heads wider than the neck. Coloration and pattern are highly variable range-wide. In North Carolina, dorsal coloration may be reddish, brown, dark- or light-green, or gray, with darker areas forming one or two rows of spots, squares, crossbars, or a checkerboard pattern down the body. Most have a yellow, tan, or white dorsal stripe running the length of the body, along with pale ventrolateral stripes on scale rows 2 and 3 that often fade into the ventral coloration. The venter can be gray, green, blueish, or yellow, often with black spots most pronounced along the edges of the ventral scales. Typically, there are two light spots on the parietal scales at the back of the head, and distinct dark crossbars separating the supralabial scales. The underside of the head is usually pale, with the dorsal aspect darker.
Morphological Features: Common Gartersnakes typically have 19 keeled scale rows at midbody, reducing to 17 posteriorly. Ventral counts range from 128-178 (131-153 in NC specimens; Palmer and Braswell, 1995), with 52-97 subcaudals (52-80) and an undivided anal plate. Head scale counts are variable, but typically as follows: 7 supralabials, 10 infralabials, 1 loreal, 2 nasals, 1 preocular, 3 postoculars, and 1+2 temporals. Palmer and Braswell (1995) noted some variation in scalation across multiple specimens in NC.

These are typically medium-sized snakes, with a maximum recorded total length of 137.2 cm (54 inches), though most are shorter. Palmer and Braswell (1995) reported a 112.4 cm female specimen from NC. Tails account for up to 28% of total length. Adult males are smaller in size and weight than adult females.

Common Gartersnakes have enlarged posterior teeth and Duvernoy's glands, meaning they are capable of producing a weak venom to aid in prey capture. This venom does not pose a threat to humans or pets; however, Gartersnakes will often attempt to bite when handled, as well as expel potent musk in an attempt to escape predators.
Technical Reference: Palmer and Braswell (1995); Ernst and Ernst (2003)
Field Guide Descriptions: Palmer and Braswell (1995); Ernst and Ernst (2003); Beane et al. (2010).
Online Photos:    Google   iNaturalist   GBIF
Observation Methods: Common Gartersnakes may be incidentally encountered under cover objects or active both day and night. They can also be found crossing roads.
Distribution in North Carolina
County Map: Clicking on a county returns the records for the species in that county.
Key Habitat Requirements
Habitat: Although Eastern Garter Snakes are most common around the edges of bogs, ponds, and other wetlands they can be found in most terrestrial habitats in the state, with only the most xeric habitats unused (Palmer and Braswell, 1995; Beane et al., 2010).
Life History and Autecology
Breeding and Courtship: Male Gartersnakes reach sexual maturity at body lengths of approximately 38 cm; females at approximately 50 cm (Ernst and Ernst, 2003). Mating may occur from early spring to summer (March to June).
Reproductive Mode: Gartersnakes are viviparous; young are born June to November, but typically August to September. Litters average 27–34 neonates, and larger females produce larger litters.

Neonates average approximately 18 cm in total length and weigh an average of 2 g.
Terrestrial Life History: Gartersnakes can be found in almost all habitats statewide, especially grassy areas, meadows, forests, and damp or mesic environments. As noted by Ernst and Ernst (2003), it is likely the most well-studied reptile in North America. They are active diurnally and nocturnally, but often found sheltering under objects or within logs during the hottest portions of the day. At night, they will often cross roads between habitats. They are among the most cold-tolerant of our native species, often active earlier and later in the year than other species. In the coldest parts of the winter, they will hibernate—often communally—in rock crevices, ant mounds, mammal burrows, and other places. Gartersnakes have been recorded in every month in North Carolina, with most activity in summer and early fall, June–October.

Home range estimates are not known from North Carolina. In Michigan, Carpenter (1952) suggested home ranges were less than 0.8 hectares (80,000 m2); in Kansas, Fitch (1999) reported average home ranges of 0.72 ha for adult males, 0.54 ha for adult females, and 0.21 ha for juveniles.
General Ecology
Adverse Environmental Impacts
Status in North Carolina
NHP State Rank: S5
Global Rank: G5

Photo Gallery for Thamnophis sirtalis - Common Gartersnake

39 photos are available. Only the most recent 30 are shown.

Recorded by: Robert Russo
Burke Co.
Comment: 		Recorded by: Guy McGrane
Watauga Co.
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Recorded by: Robert Russo
Avery Co.
Comment: 		Recorded by: Robert Russo
Avery Co.
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Recorded by: Robert Russo
Caldwell Co.
Comment: 		Recorded by: Robert Russo
Caldwell Co.
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Recorded by: K. Bischof
Transylvania Co.
Comment: 		Recorded by: K. Bischof
Transylvania Co.
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Recorded by: Robert Russo
Caldwell Co.
Comment: 		Recorded by: Robert Russo
Caldwell Co.
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Recorded by: Pat Momich
Madison Co.
Comment: 		Recorded by: Gary Williamson, Byron Carmean, Dillion Kania, Todd Pusser and Steve Hall
Durham Co.
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Recorded by: Robert Russo
Alexander Co.
Comment: 		Recorded by: Robert Russo
Alexander Co.
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Recorded by: Robert Russo
Alexander Co.
Comment: 		Recorded by: Robert Russo
Caldwell Co.
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Recorded by: Robert Russo
Caldwell Co.
Comment: 		Recorded by: J. Mickey
Wilkes Co.
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Recorded by: Erich Hofmann and Kayla Weinfurther
Buncombe Co.
Comment: 		Recorded by: C. Teague, B. Bockhahn, C. Blake
Beaufort Co.
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Recorded by: K. Bischof
Transylvania Co.
Comment: 		Recorded by: K. Bischof
Transylvania Co.
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Recorded by: B. Covington
Moore Co.
Comment: 		Recorded by: J. Mickey
Alleghany Co.
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Recorded by: Robert Russo
Wilkes Co.
Comment: 		Recorded by: Robert Russo
Wilkes Co.
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Recorded by: Robert Russo
Alexander Co.
Comment: 		Recorded by: Robert Russo
Alexander Co.
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Recorded by: Erich Hofmann
Craven Co.
Comment: 		Recorded by: Erich Hofmann
Craven Co.
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